1. Field of the Invention
The present invention concerns wireless communications, and more specifically, to an apparatus and method of expanding coverage in IEEE 802.11ah.
2. Related Art
Coverage expansion is a key requirement that allows IEEE 8002.11ah to be achieved. Coverage expansion is demanded a lot in most of 802.11ah applications, particularly in smart grid, outdoor sensor network (over an area of 1 km*1 km), and expanded range of Wi-Fi (which covers a broad area such as a department store or campus).
802.11ah FR-EM specifies a data rate of 100 kbps or more with a radius of 1 km as requirements in the physical SAP. Recently, standardization organizations such as 3GPP MTC or IEEE 802.16n (GRIDMAN)/16p, 802.15.4 g, requests submission of results analyzed by range estimators that may be referred to by the NIST (National Institute of Standards and Technology) regarding which communication technology, in light of coverage and average throughput, is more suitable for smart grid applications.
However, coverage expansion may be difficult to attain in 802.11ah. For example, since multiple STAs (stations) are highly likely to be single-antenna devices for power savings, the coverage is generally limited by the uplink range. The coverage may also be restricted by the transmission power regulation policy of the nation (e.g., China or Japan).
Moreover, in IEEE 802.11ah, the repetition counts have been set as two primarily in consideration of indoor M2M (machine to machine) applications, and this renders it difficult to secure enough coverage. Accordingly, there is a need for an apparatus and method that may provide sufficient coverage in IEEE 802.11ah, that is, an apparatus and method for coverage expansion.